Water heaters are used in homes, businesses and just about any establishment having the need for heated water. A conventional tank-style water heater has a water heater tank, and at least one heating element or “heater” for heating the water in the water heater tank. The heater is often a gas-fired burner and/or electric heating element. A water heater typically also includes a thermostat or controller for controlling the heater. The controller typically receives signals related to the temperature of the water within the water heater tank, often from a temperature sensor or the like that is thermally engaged with the water in the water heater tank.
In some instances, the water heater may operate in accordance with a first temperature set point and a second temperature set point. The difference between the first and second temperature set point is often referred to as the temperature differential of the water heater. When temperature signals from the temperature sensor indicate that the water temperature is below the second set point, for example when the water temperature is below about 120° F., the controller may turn on the heater and the water within the water heater tank begins to heat. After some time, the water temperature within the water heater tank will increase to the first set point, which, for example may be about 140° F. At this point, the controller may cause the heater to reduce its heat output or, alternatively, causes the heater to turn off. This heat cycle begins again when the water temperature within the water heater tank cools down below the second set point.
For a gas fired water heater, a temperature sensor, a gas valve and a controller are often mounted to the water heater tank. The controller typically receives a temperature signal from the temperature sensor. In some cases, the temperature sensor may protrude into and thermally engage the water in the water heater tank. The controller typically is programmed to control the gas valve such that the temperature of the water in the water heater tank remains between the first and second temperature set points, as described above. For an electric water heater, a temperature sensor, a power delivery unit and a controller may be mounted to the water heater tank. In this case, the controller may control the power delivery unit such that the temperature of the water in the water heater tank is kept between the first and second temperature set points.
In some instances, sediment may build-up in tank-style water heaters at a rate determined by the quality of the water. Sediment build-up often creates a mineral rich slurry at the bottom of the tank. This slurry typically has a high heat capacity and is heavier than water. When the burner is running, this sediment can absorb a great deal of heat from the heat exchanger as the heat is passed from the tank metal to the water. In many cases, end-users are asked to periodically drain their tank to remove this sediment build-up in order to prevent damage to the water heater and/or increase efficiency of the water heater. In some cases, failure to remove excessive sediment can result in over-heated metal and damage to the glass lining of the water storage tank, which can reduce the life of the tank. What would be desirable is a mechanism for detecting the build-up of sediment so that end-users can be notified when sediment build-up has occurred. Alternatively, or in addition, it would be desirable to compensate the operation of the water heater to account for sediment build-up.